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    <!-- 【案例】统计数组中元素出现的次数
    [1,2,3,1,1,1,2,2,3,3,4]
    1出现的次数 4
    2出现的次数 3
    3出现的次数 3
    4出现的次数 1 -->
    <script>
        var arr1=[1,2,3,1,1,1,2,2,3,3,4];
        var res=arr1.reduce(function(pre,cur){
            if(cur in pre){
                pre[cur]=pre[cur]+1;
            }else{
                pre[cur]=1;
            }
            return pre
        },{})

        for(var key in res){
            console.log(key+'出现的次数'+res[key]+'次')
        }
    </script>
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